(1) Field of the Invention
The invention relates to interconnect techniques in an integrated circuit device, and more particularly, to a very low resistivity interconnection method and structure using bonded metal wires.
(2) Description of the Prior Art
Internal interconnects of integrated circuit devices are typically formed using metal films that have been deposited and patterned. These metal films provide low resistivity connections between the various active and passive devices and layers in the circuit. In certain applications, such as high power devices, the resistivity of the metal film lines is too large.
Referring now to FIG. 1, an exemplary prior art integrated circuit is illustrated in cross section. In this example, two MOS transistors 34 and 38 are formed on a substrate 10. The transistors 34 and 38 have source/drain regions A, B, and C14 comprising a patterned diffusion layer 14 in the substrate 10. In this example, the circuit requires that source/drain regions A and B be coupled together through a low resistivity path while region C is not connected to A and B. To form the coupling path, a first metal layer 22 contacts the source/drain regions 14. A second metal layer 30 contacts the first metal layer 22 and couples region A to region B via the bridge 54 of second metal layer 30. A first metal layer section 50 contacts the C region.
Referring now to FIG. 2, a simplified model of the prior art example circuit is shown. The model shows the coupling metals sections as resistors RMETAL1 50 and RMETAL2 54. The resistance between nodes A and B is the resistance of the first and second metal paths including the bridge 54. This resistance RMETAL2 54 depends on the resistivity characteristics of the deposited metal film. If the resistance is too high, it can only be made lower by increasing the width of the metal connection. However, space limitations on the circuit die restrict the metal size. In addition, the presence of the C region eliminates the use of the first metal layer as a parallel interconnect path for A and B. In a high power application, where a large current flow may cause a large IR drop, the integrated circuit process may not be capable of creating an interconnect of low enough resistance using the available metal film layers.
Several prior art inventions describe the application of bonded wire to integrated circuit devices. U.S. Pat. No. 5,032,889 to Murao et al describes a wafer-scale integrated circuit device where functional blocks on the wafer are interconnected using a combination of metal layer lines on the IC and bonding wires to thereby improve reliability. U.S. Pat. No. 5,869,357 to Zambrano discloses a metallization and wire bonding process for a power semiconductor device.